To address the key problems in ultra-high voltage flexible DC transmission system that the core biaxially oriented polypropylene (BOPP) films for dry-type DC capacitors rely on imports, and the high ash content of domestic polypropylene resins leads to insufficient insulation and ageing resistance of the films, we selected imported electrical-grade, domestic continuously washed low-ash, and domestic unwashed high-ash polypropylene resins to prepare BOPP films. The microscopic morphology, crystal structure and electrical properties of the films were characterized systematically, and the combined electro-thermal ageing tests under AC-DC superimposed conditions were conducted. The results show that BOPP films prepared from low-ash domestic washed polypropylene resin have higher electric strength and more stable high-temperature dielectric performance. Moreover, the crystal structure of the films has no significant changes after ageing, and their electrical properties are close to those of the imported BOPP films.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |